1. Field of the Invention
The present invention relates to molding a battery, and more particularly, the present invention relates to a mold for a battery and a method of molding a battery, such as a secondary battery, using the mold, wherein a minimum amount of a molding substance, such as a resin, is used to retain a board, such as a protective circuit board, on the battery, resulting in the molding time using the resin being shortened and a safety vent of a battery can being prevented from being fractured by high pressure during a molding process.
2. Description of the Prior Art
As generally known in the art, a secondary battery, particularly a square-type lithium ion secondary battery electrically connects a protective circuit board to the positive and negative terminals of a can (battery sheath), in order to protect the battery from overcharging, over-discharging, an over-current, a short due to an external load, and the like. The can has a safety vent, which has a smaller wall thickness than that of the remainder of the can, formed on a side of the negative terminal so that if abnormal pressure occurs, the safety vent is fractured and internal gas is discharged to the exterior.
Both the can and the protective circuit board are contained in a sheath cover, which is composed of an upper cover and a lower cover, and are shipped as a product, in order to enhance the mechanical coupling strength between the can and the protective circuit board and protect them from external environments.
Recently, a method has been used wherein the gap between the can and the protective circuit board is filled with a resin or wherein the can and the protective circuit board are completely coated with a resin, in order to reduce the number of parts and improve the productivity. For example, upper and lower molds are provided with cavities, in which cans and protective circuit boards are to be contained, and gates and runners, which are connected to the cavities and act as channels for the resin during filling. Both the cans and the protective circuit boards are then seated on the cavities of the upper and lower molds and a resin, which has high temperature and high pressure, is injected toward the cavities through the runners and the gates, which are in communication with the runners. As a result, the cans and protective circuit boards are firmly mechanically retained by the resin.
However, such molds have a problem in that the runners, which act as channels for the resin, are formed a great distance away from the cavities and the amount of resin, which remains in the runners and the gates, is larger than that which is used to fill the gap between the cans and the protective circuit boards. This wastes the resin. In particular, after the resin molding is completed and the batteries are removed from the molds, the resin, which remains in the runners and the gates of the molds, is in a hardened state. Consequently, the expensive resin, which cannot be reused, must be removed from the runners and gates and disposed of.
In addition, it takes a long time for the resin to reach the cavities, because the runners are positioned away from the cavities and are very long. This prolongs the filling time. It is also likely that the cavities, in particular, the gap between the cans and the protective circuit boards, are not completely filled with the resin and the process ends in that state. This results in a poor molding of the secondary battery.
Conventional resin molding methods also have a problem in that, since the safety vent of the can is positioned farther from the gate into which the resin is injected, the safety vent is vulnerable to fracture due to the resin filling pressure. This is because the farther from the gate into which the resin flows, the higher the air pressure due to the resin filling becomes, and the safety vent, which has a smaller wall thickness than that of the remainder of the can, can be fractured toward the interior of the can by such high pressure.
If the safety vent is fractured in this way, a secondary problem can occur, i.e., the resin at a high pressure can penetrate into the can, and the electrolyte can easily leak to the exterior along the interface between the can and the resin during use of the battery.